In recent years, indoor wireless coverage is increasingly becoming a hot spot in the technical field of wireless communications, wherein researches on antenna technologies draw particular concerns in the industry.
The researches up to date have already indicated that due to advantages of circularly-polarized waves compared with linearly-polarized waves, e.g., eliminating multi-path fading and being insensitive to polarization direction, circularly-polarized antennas are widely used in satellite communication and broadcasting. Furthermore, recent work further finds that the circularly-polarized antennas may also be used to enhance indoor coverage because the circularly-polarized antennas are capable of reducing the influence of the polarized direction of a user terminal's antenna on the received signal-to-noise ratio.
However, most of existing circularly-polarized antennas are non-omni directional, e.g., a corner-truncated square patch antenna, a dual/four feed patch antenna and a spiral antenna, etc. Due to their directional radiation patterns, these antennas are not suitable for indoor wireless coverage. Furthermore, these antennas suffer from narrow bandwidth and complex structure.
In FM and TV broadcasting bands, there are several classical types of omni directional circularly-polarized antennas, such as Lindenblad and cycloid dipole antennas. However, if these antennas are scaled down to the commonly-used band (0.8-2.5 GHz) for the indoor wireless coverage, they will be too large in size and very unstable in structure and thereby become unpractical.
Therefore, it is desirable to provide a new omni directional circularly-polarized antenna, which has characteristics such as a wide axis ratio bandwidth and a simple and stable structure, and meanwhile may operate in commonly-used wireless bands to achieve indoor wireless coverage.